Radiologists and others use a number of methods to create images of structures within a patient's body to help diagnose diseases and guide therapeutic procedures. Methods used include, for example, conventional X-Ray, Computerized Tomography ("CT"), ultrasound, Positron Emission Tomography ("PET"), and (Nuclear) Magnetic Resonance Imaging ("NMR" or "MRI"), among others. These methods respectively employ X-radiation (both the X-Ray and CT methods), sound, radio active emissions, and magnetic fields in combination with radio-frequency electromagnetic radiation, to create images of structures within the patient's body.
When creating such diagnostic images of a patient, it is desirable to use surface anatomical features which are visible both on the patient and on the diagnostic image of that patient as reference points to facilitate the performance of surgical or other therapeutic intervention techniques. Reference points defined on both a patient's body and a diagnostic image of interior features of that patient's body, allow a physician to geometrically calculate the precise location of a particular site within the patient's body or a particular position of a specific structure within the patient's body. Pin-pointing the location of a particular site or structure allows the physician to more easily and accurately biopsy or otherwise treat the area.
However, there often are no surface anatomical features on the patient's body adequate to use as such reference points (e.g. such features may not exist or may not be located appropriately for such use). If there are no anatomical reference points on the surface of the patient's body, one is unable to precisely locate a target site or structure shown in a two dimensional diagnostic image. The location of the target site or structure is obscure because the two-dimensional diagnostic image does not provide sufficient information for a geometric relationship between a surface point on the patient's body and the target site or structure to be accurately calculated (i.e. it is unclear at what point on the patient's body the diagnostic image scan was taken).
In such cases, it is desirable to place artificial reference markers on the patient's skin to serve as reference points. A physician may place artificial markers in positions which are optimal reference points relative to the location of target tissues within the patient's body. The markers are designed to clearly show unique and identifiable reference points on both the surface of the patient's body and on the diagnostic image.
In addition, it is becoming increasingly important to align images formed by different imaging methods to better identify pathologic structures. Aligning, or "rectifying," images and other radiographic data formed by different imaging methods would be substantially improved (in both ease and accuracy) through the use of surface markers which create reference points visible to a multiplicity of imaging methods. Such surface markers would facilitate the precise superimposition of imaging data from CT, MRI, and other sources for optimal correlation of tissues and physiologic processes which are demonstrated using these various methods.
Furthermore, it is desirable to provide reference markers of consistent shapes and sizes to facilitate the above described calculations and methods.
Imaging with X-radiation (X-rays and CT scans) requires that a reference marker comprise a material which impedes the transmission of radiation at the wavelength used in commercial machines. Metals and materials which contain metal salts are popular for these techniques. However, certain organic materials, and other non-metallic materials also have adequate opacity.
A reference marker for use with MRI depends on entirely different properties. With this modality, a powerful magnetic field is applied which orients the rotational axis of atomic nuclei along a single vector. Upon removal of the magnetic field, the spinning nuclei revert to a random distribution of axial orientation. In the process of reverting the nuclei emit radiation at characteristic frequencies. By detecting this radiation a computer, using mathematical formulae, can compose an image based on the different intensities from different tissues.
Reference markers for use with MRI require mobile atomic nuclei in a liquid state. Commercial MRI machines also detect frequencies and intensities of radiation typically emitted from aqueous solutions or composites. Certain organic compounds also emit frequencies detectable by commercial machines. Therefore, it is important that markers retain atomic nuclei in an aqueous state (e.g. it is important that markers do not lose water) to be dense to MRI.
Surface markers of various shapes and sizes are generally shown in the prior art. However, such prior art surface markers are inadequate to address the problems described above. There is no surface marker disclosed which is satisfactorily visible to a variety of imaging methods. For example, one commercial product today uses a small, dense metal bead attached to adhesive tape. The metal is dense to X-radiation and the adhesive allows rapid, secure attachment to the patient's skin. However, the metal produces an imaging artifact at certain useful X-radiation intensities and it is transparent to methods such as MRI. Moreover, with MRI an aberration is produced which obscures adjacent tissue, rendering the image useless. Therefore, this surface marker is not satisfactory.
It would be useful to have a marker which is dense to all of the commonly used imaging methods, which does not produce aberrations that obscure portions of the image, and which is available in consistent and reliable shapes and sizes.